Human embryonic stem cells (hESCs) can undergo unlimited self-renewal and differentiate into all the cell types in the human body, and thus hold great promise for cell replacement therapy. However, one major problem for hESC-based therapy is that the cells derived from hESCs will be rejected by the recipient and can only be tolerated under persistent immunosuppression, which itself can cause cancer and infection. Recent development of induced pluripotent stem cells (iPSCs), which are generated from somatic cells of individual patient with defined factors and very similar to hESCs, could provide ideal cell source for transplantation by avoiding graft rejection in the patient. In addition, the disease-specific iPSCs can be used as human disease models for more reliable testing of the efficacy and toxicity of drugs. However, there are several major bottlenecks that prevent the development of iPSCs in human therapy and drug discovery. The overall goal of this proposal is to resolve the major bottlenecks remained in human iPSC biology to make it feasible for human therapy and drug discovery. We propose to develop safe and efficient approach to generate iPSCs from human patients. We propose to develop strategies to eliminate the risk of teratomas associated with the undifferentiated iPSCs. We propose to develop mouse model with functional human immune system to study the immune responses and tolerance during transplantation. Resolving these bottlenecks will greatly facilitate the development of hESCs into stem cell therapy and disease models for drug discovery.

Statement of Benefit to California:

Diabetes and heart diseases remain the most costly diseases in our State and Nation. In the case of diabetes, 1 of every 10 Californians (2.7 million) were afflicted with diabetes in 2007, costing the State $24.5 billion annually. There is a significant increase in the occurrence of both types of diabetes in youths under 18 years of age (0.16% of youth <18 yr have type 1 diabetes nationally). Simply put, diabetes is having devastating consequences on both those afflicted and on State/National healthcare costs, and, given the staggering rise in both occurrence and costs, diabetes possesses the potential to completely overwhelm our healthcare system. There remains an urgent and critical need for a cell-based cure of diabetes. There is hope, since transplantation of functional β cells from human donors has been validated clinically to cure diabetes.
While significant progress has been made in the derivation of functional β cells and cardiomyocytes from human ES cells, these allogenic cells will be rejected by the recipient upon transplantation unless the immune system of the recipient is persistently suppressed. However, immune suppression itself has severe consequences with significantly increased risk of cancer and infection. This problem might be resolved by the recent breakthrough in induced pluripotent stem cell (iPSCs), which can be reprogrammed from somatic cells of human patients by defined factors and thus can provide a renewable source of autologous cells for transplantation. In addition, the disease-specific iPSCs will provide the much needed disease models to more reliably predict the drug responses in humans. With our significant progress in producing iPSCs without viral vectors or permanent genetic modification, our proposed research will resolve the major bottlenecks that hinder the development of iPSCs into human therapy and drug discovery. If successful, the funding spent now on research is nominal when compared to the billions that will be saved in treatment costs and the improved quality of life for patients.

Review Summary:

The overall goal of this project is to develop safer human pluripotent cell lines for clinical use. The applicants propose to generate human induced pluripotency stem cells (iPSC) using an approach that combines the use of vectors with small molecules that stimulate the efficiency of iPSC production. As proof of concept, the applicants will use their new method to generate iPSC from type I diabetic patients, differentiate them into beta cell precursors and evaluate the ability of these transplanted cells to normalize glucose levels in diabetic mice. The applicants will determine the frequencies of teratoma formation in transplanted mice and also develop a genetic approach to efficiently eliminate undifferentiated iPSC during lineage-specific differentiation. In the final aim, this group will test the immunological consequences of autologous iPSC transplantation using a mouse model with a humanized immune system.
This application addresses three bottlenecks to the development of iPSC for therapeutic use: potential oncogenicity of reprogramming factors delivered by integrating retroviruses, risk of teratoma formation from residual iPSC and the lack of a model to assess immunological responses to iPSC derivatives. The research plan, while ambitious, was well presented. Strong preliminary data including iPSC generation with the proposed methods and successful homologous recombination in hESC illustrate feasibility of the approach. As transplantation of pancreatic beta cell precursors has historically generated teratomas in vivo, use of this population to treat diabetes enables determination of both therapeutic effect and tumorigenicity. However, one reviewer felt these studies weren’t well integrated into the proposal. While full responsiveness of the T-cells matured in the model’s fetal thymus must be demonstrated, the development of a mouse model with a humanized immune system and the team’s inclusion of a leader in immunology with published experience generating such models did strengthen the proposal. Reviewers did note that the proposal would benefit from more discussion of pitfalls and alternative approaches.
Reviewers universally praised the strength of the Principal Investigator’s (PI’s) experience in the field, publication record and the first rate assembly of collaborators for the project. The strong team makes success likely. Reviewers expressed concern that the PI may be overextended. In addition, the reviewers raised concerns about the proposal’s budget. Individual roles of the large number of investigators participating in the project, in particular that of the subcontractor responsible for the small molecule screens, should be more thoroughly defined and justified. The research environment is outstanding and available resources at the applicant’s institution are exceptional.
This proposal, addresses three major bottlenecks to translating iPSC from novel research observation to therapeutic candidate: insertional mutagenesis, teratoma formation from residual undifferentiated cells and the lack of models to predict whether iPSC are truly immuno-privileged. Findings from this work should be applicable to the entire iPSC field.
PROGRAMMATIC REVIEW
During programmatic review, the Grants Working Group was instructed to consider the specific rank order of all applications in Tier I as an indicator of priority for funding. A motion was made to change the rank order of this application from 15 to 14 within Tier I as it addresses several bottlenecks of concern to CIRM’s mission. Reviewers felt that the proposed humanized mouse model is particularly important. The motion to change the rank order of this application carried.